Implement introspection with __signature__ package

The signature module was turned into a package under
'PySide2/support/signature'. The package is completely isolated
so that nothing is leaking into the normal import machinery.

The package is also not initialized unless a __signature__ attribute
is accessed. The only change to Python during a PySide run is
the existence of the __signature__ attribute.

As a side effect, all tests run at the same speed as before
this extension.

The module does not actively import PySide modules. Instead,
it inspects sys.modules and reloads its mapping.py if needed.

Example usage:

>>> PySide2.QtWidgets.QGraphicsAnchorLayout.addAnchors.__signature__
>>> PySide2.QtWidgets.QGraphicsAnchorLayout.__signature__

The module has been thoroughly tested on macOS.
I consider this ready.

Task-number: PYSIDE-510
Change-Id: Ibb231a7fbb4ccc1a7249df55e3881a4e21a19c0d
Reviewed-by: Christian Tismer <tismer@stackless.com>

1 files changed, 115 insertions, 0 deletions

diff --git a/sources/pyside2/PySide2/support/signature/loader.py b/sources/pyside2/PySide2/support/signature/loader.py
new file mode 100644
index 000000000..f9c8b5c53
--- /dev/null
+++ b/sources/pyside2/PySide2/support/signature/loader.py
@@ -0,0 +1,115 @@
+#############################################################################
+##
+## Copyright (C) 2017 The Qt Company Ltd.
+## Contact: https://www.qt.io/licensing/
+##
+## This file is part of PySide2.
+##
+## $QT_BEGIN_LICENSE:LGPL$
+## Commercial License Usage
+## Licensees holding valid commercial Qt licenses may use this file in
+## accordance with the commercial license agreement provided with the
+## Software or, alternatively, in accordance with the terms contained in
+## a written agreement between you and The Qt Company. For licensing terms
+## and conditions see https://www.qt.io/terms-conditions. For further
+## information use the contact form at https://www.qt.io/contact-us.
+##
+## GNU Lesser General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU Lesser
+## General Public License version 3 as published by the Free Software
+## Foundation and appearing in the file LICENSE.LGPL3 included in the
+## packaging of this file. Please review the following information to
+## ensure the GNU Lesser General Public License version 3 requirements
+## will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+##
+## GNU General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU
+## General Public License version 2.0 or (at your option) the GNU General
+## Public license version 3 or any later version approved by the KDE Free
+## Qt Foundation. The licenses are as published by the Free Software
+## Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+## included in the packaging of this file. Please review the following
+## information to ensure the GNU General Public License requirements will
+## be met: https://www.gnu.org/licenses/gpl-2.0.html and
+## https://www.gnu.org/licenses/gpl-3.0.html.
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+from __future__ import print_function, absolute_import
+
+"""
+This file was originally directly embedded into the C source.
+After it grew more and more, I now prefer to have it as Python file.
+The remaining stub loader is a short string now.
+
+The loader has to lazy-load the signature module and also provides a few
+Python modules that I consider essential and therefore built-in.
+This version does not use an embedded .zip file.
+"""
+
+import sys
+import os
+import functools
+from contextlib import contextmanager
+from distutils import sysconfig
+
+@contextmanager
+def add_path(path):
+    sys.path.insert(0, path)
+    yield
+    sys.path.pop(0)
+
+# Make sure that we always have the PySide containing package first.
+# This is crucial for the mapping during reload in the tests.
+package_dir = __file__
+for _ in "four":
+    package_dir = os.path.dirname(package_dir)
+assured_site_packages = functools.partial(add_path, package_dir)
+
+with assured_site_packages():
+    if sys.version_info >= (3,):
+        from PySide2.support.signature import inspect
+        from PySide2.support.signature import typing
+    else:
+        import inspect
+        namespace = inspect.__dict__
+        from PySide2.support.signature import backport_inspect as inspect
+        inspect.__dict__.update(namespace)
+    from PySide2.support.signature import parser
+# Note also that during the tests we have a different encodind that would
+# break the Python license decorated files without an encoding line.
+
+# name used in signature.cpp
+def pyside_type_init(*args, **kw):
+    with assured_site_packages():
+        return parser.pyside_type_init(*args, **kw)
+
+# name used in signature.cpp
+def create_signature(props, sig_kind):
+    if not props:
+        # empty signatures string
+        return
+    if isinstance(props["multi"], list):
+        return list(create_signature(elem, sig_kind)
+                    for elem in props["multi"])
+    varnames = props["varnames"]
+    if sig_kind == "method":
+        varnames = ("self",) + varnames
+    elif sig_kind == "staticmethod":
+        pass
+    elif sig_kind == "classmethod":
+        varnames = ("klass",) + varnames
+    else:
+        raise SystemError("Methods must be normal, staticmethod or "
+                          "classmethod")
+    argstr = ", ".join(varnames)
+    fakefunc = eval("lambda {}: None".format(argstr))
+    fakefunc.__name__ = props["name"]
+    fakefunc.__defaults__ = props["defaults"]
+    fakefunc.__kwdefaults__ = props["kwdefaults"]
+    fakefunc.__annotations__ = props["annotations"]
+    return inspect._signature_from_function(inspect.Signature, fakefunc)
+
+# end of file